C++ :

#include <cstdio>
int main(){
    int x, y; if(scanf("%d %d", &x, &y) != 2) return 0;
    /* 只能向下或向右：从 (0,0) 到 (x,y) 的路径数 = C(x+y, x)
       x,y <= 10 -> x+y <= 20，用递推表算组合数 */
    long long c[32][32];
    for(int i=0;i<=x+y;i++){
        c[i][0] = 1;
        for(int j=1;j<=i;j++)
            c[i][j] = (j == i) ? 1 : c[i-1][j-1] + c[i-1][j];
    }
    printf("%lld\n", c[x+y][x]);
    return 0;
}